U.S. patent application number 11/647921 was filed with the patent office on 2008-07-03 for device and method for mounting an object on a bone.
Invention is credited to Steven Jacobson, Craig M. McAllister.
Application Number | 20080161814 11/647921 |
Document ID | / |
Family ID | 39585048 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080161814 |
Kind Code |
A1 |
McAllister; Craig M. ; et
al. |
July 3, 2008 |
Device and method for mounting an object on a bone
Abstract
A device for removable attachment to a bone of a living patient,
useful as a mounting support for a trackable part of a computerized
surgical navigation system and a method for attaching an object
removably to a bone of a living patient. A shaft having a self
drilling, self-tapping screw tip can be inserted transversely of
the bone and securely screwed into the cortex. A screw drives a
sharp-edged sleeve along the shaft to engage the near cortex. A
stepping mechanism allows incremental angular movement of a portion
of an adjustment mechanism and indicates when the sleeve is
securely engaged by resisting further tightening.
Inventors: |
McAllister; Craig M.;
(Kirkland, WA) ; Jacobson; Steven; (Dupont,
WA) |
Correspondence
Address: |
CHERNOFF, VILHAUER, MCCLUNG & STENZEL
1600 ODS TOWER, 601 SW SECOND AVENUE
PORTLAND
OR
97204-3157
US
|
Family ID: |
39585048 |
Appl. No.: |
11/647921 |
Filed: |
December 28, 2006 |
Current U.S.
Class: |
606/83 ; 606/53;
606/80; 606/96 |
Current CPC
Class: |
A61B 2090/3916 20160201;
A61B 2090/031 20160201; A61B 2090/3991 20160201; A61B 17/86
20130101; A61B 2090/035 20160201; A61B 2017/8655 20130101; A61B
17/8635 20130101; A61B 2090/3983 20160201 |
Class at
Publication: |
606/83 ; 606/53;
606/80; 606/96 |
International
Class: |
A61B 17/00 20060101
A61B017/00; A61B 17/56 20060101 A61B017/56; A61B 17/58 20060101
A61B017/58 |
Claims
1. A device for mounting an object removably on a bone, comprising:
(a) a central shaft having a distal end portion; (b) a threaded tip
included in said distal end portion; (c) a bone-engaging member
disposed on and movable longitudinally along said central shaft,
said bone-engaging member having a bone-gripping distal end; and
(d) an adjustment mechanism mounted on said central shaft and
arranged to move said bone-engaging member controllably toward said
distal end of said central shaft.
2. The device of claim 1 including a coupling interconnecting said
adjustment mechanism with said bone-engaging member and keeping
said adjustment mechanism within a predetermined distance from said
bone-engaging member.
3. The device of claim 2 wherein said bone-engaging member includes
a sleeve disposed slidably on said central shaft and wherein said
sleeve has a groove defined adjacent a proximal end thereof and
said adjustment mechanism includes a rotatable member mounted on
and rotatable about said central shaft and including a groove
defined adjacent a proximal end thereof, and wherein said coupling
includes a coupling member disposed adjacent said proximal end of
said sleeve and said distal end of said rotatable member and
including respective catches engaged in each of said grooves.
4. The device of claim 1 wherein said threaded tip includes a
drill.
5. The device of claim 1 wherein said threaded tip includes
self-tapping screw threads.
6. The device of claim 1 wherein said threaded tip includes a
self-drilling, self-tapping screw.
7. The device of claim 1 wherein said bone-engaging member is
movable longitudinally along said central shaft but is prevented
from rotating about said central shaft.
8. The device of claim 1 wherein said adjustment mechanism includes
a rotatable member engaged with an external thread on said central
shaft and a rotary coupling connecting said rotatable member with
said bone-engaging member.
9. The device of claim 1 wherein said bone-engaging member is a
sleeve including a longitudinally-extending slot and wherein a
slot-engaging member extends radially from said central shaft and
is engaged in said slot, thereby preventing said sleeve from
rotating about said central shaft.
10. The device of claim 1 wherein said adjustment mechanism
includes a rotatable member engaged with an external thread on said
central shaft and said bone-engaging member and said rotatable
member have respective cooperative elements of a torque-indicating
mechanism.
11. The device of claim 10 wherein said torque-indicating mechanism
includes a stepping mechanism.
12. The device of claim 11 wherein said stepping mechanism includes
corresponding inclined facets defined respectively on the proximal
end of the bone-engaging member and the distal end of the rotatable
member and wherein corresponding ones of said facets are engageable
with each other at selected angles of rotation of said rotatable
member.
13. The device of claim 1 wherein said distal end portion includes
a shoulder projecting radially outward adjacent said threaded
tip.
14. The device of claim 1 wherein said distal end portion is
externally threaded along a portion thereof extending in a proximal
direction from said threaded tip.
15. The device of claim 14 wherein said threaded tip is
self-tapping and gradually increases in diameter toward and merges
with said externally threaded portion of said distal end
portion.
16. A method of releasably fastening an article to a bone,
comprising: (a) boring and tapping a first hole inwardly through a
cortex of a bone; (b) screwing a threaded distal end portion of a
shaft into an interior of said bone through said first hole and
placing a tip of said distal end portion into contact with an
opposite interior surface of said cortex of said bone; (c)
thereafter, sliding a bone-engaging member longitudinally along
said shaft and thereby bringing a bone-gripping distal end of said
bone-engaging member into contact against said cortex of said bone
adjacent said first hole and forcing said distal end of said
bone-engaging member into gripping engagement with said cortex of
said bone; and (d) mechanically holding said bone-engaging member
in a predetermined angular position with respect to said shaft so
as to prevent rotation of said bone-engaging member about said
shaft and to keep said distal end of said bone-engaging member in
gripping engagement with said cortex of said bone, thereby
preventing rotation of said shaft with respect to said bone.
17. The method of claim 16 wherein said bone-engaging member
includes a sleeve disposed slidably on said shaft, including the
step of preventing said sleeve from rotating about said shaft while
said sleeve slides longitudinally along said shaft.
18. The method of claim 16 wherein said step of moving said sleeve
longitudinally along said shaft includes the step of rotating an
adjustment member along a helical thread defined on said shaft and
thereby urging said distal end of said bone-engaging member into
gripping engagement with said cortex of said bone.
19. The method of claim 16, including the step of using a
multi-faceted ramp stepping mechanism to determine when sufficient
force has been applied to said bone-engaging member to urge said
distal end of said bone-engaging member into gripping engagement
with said cortex of said bone.
20. The method of claim 16, including the step of coupling an
adjustment member to said bone-engaging member so as to allow said
adjustment to pull said sleeve out of gripping engagement with said
cortex of said bone.
21. The method of claim 16, including the step of engaging an
angular stepping escapement device between a rotating adjustment
mechanism and said bone-engaging member to retain said rotating
adjustment mechanism in a selected position of rotation with
respect to said bone-engaging member when said bone-engaging member
is in anchoring engagement with said cortex of said bone.
22. A method of releasably fastening an article to a bone,
comprising: (a) boring a first hole having a first diameter
inwardly through a cortex of a bone; (b) inserting a drill into an
interior of said bone through said first hole and into contact with
an interior surface of said cortex of an opposite side of said bone
and therefrom boring a second hole outward into said cortex, said
second hole having a diameter smaller that said first diameter; (c)
inserting a shaft having screw threaded tip into said bone through
said first hole and threading said screw threaded tip into said
second hole to a limited depth at which a distal end portion of
said shaft encounters said cortex, and thereby resists further
movement of said threaded tip into said second hole; (d)
thereafter, sliding a bone-engaging member longitudinally along
said shaft, thereby bringing a distal end of said bone-engaging
member into contact against said cortex of said bone adjacent said
first hole, and forcing said distal end of said bone-engaging
member into gripping engagement with said cortex of said bone; and
(e) mechanically holding said bone-engaging member in a
predetermined angular position with respect to said shaft so as to
prevent rotation of said bone-engaging member about said shaft and
to keep said distal end of said bone-engaging member in gripping
engagement with said cortex of said bone, thereby preventing
rotation of said shaft with respect to said bone.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to releasably attaching an
object to a bone in a living patient, and relates particularly to a
device for fastening an object such as a component of a
computerized surgical navigation system stably to a large bone such
as a femur.
[0002] In surgical procedures involving articulated skeletal bone
joints, such as knee replacement procedures, it is often helpful to
use computer-aided navigation, based on infrared or electromagnetic
imaging systems, to locate bones or parts of bones correctly with
respect to each other during the procedure. In order to establish
and monitor the position of a large bone as a reference for such
computer-aided navigation, a reference device must be securely and
stably, but removably, mounted on the large bone.
[0003] Attachment of objects to bones has been addressed by the
prior art, as disclosed, for example, by Glossop U.S. Pat. No.
6,203,543 and Sasso U.S. Patent Application Publication No.
US2005/0119566.
[0004] In attaching some known devices to a bone as a mounting
support for a navigation system reference target or beacon, a screw
is inserted transversely through a large bone such as the femur,
using a hole drilled entirely through the thickness of the bone. In
order to be secure the screw must be long enough to extend beyond a
shoulder or other depth-limiting stop far enough to extend into the
cortex of the bone on the far side. At the same time, however, the
screw should not be so long as to extend unnecessarily beyond the
far side of the bone when the shoulder or other stop is seated on
the near side of the bone. Accordingly, such a device must be
available in various different lengths for use with bones of
different sizes. While an estimate can be initially made of the
size of a bone, time may be wasted if a mounting device of the
wrong size is chosen initially and must be replaced.
[0005] Adjustment of some previously available devices to securely
support an object such as a part of a navigation system has
required separate operations of first drilling and thereafter
tapping screw holes in bones, taking more time than is desired
during a surgical procedure.
[0006] In other devices for anchoring an object to a bone a bone
engaging part of the device must be rotated as it is moved through
soft tissue surrounding the bone in order to bring that part of the
device into engagement against the bone. This rotary motion during
movement through the soft tissue causes undesired trauma to the
soft tissue and may delay healing in that area.
[0007] Adjusting a mounting fastening device to attach it securely
to a bone has thus been a difficult and inexact procedure in the
past.
[0008] What is desired, then, is a device and a method for its use
to attach an object securely to a large bone, and to accomplish
such attachment without taking an undue amount of time, and with a
predictable result, so as to achieve a secure attachment in a
device which is readily removable when its presence is no longer
required.
SUMMARY OF THE INVENTION
[0009] The present invention answers some of the needs mentioned
above by providing a device and a method for its use for securely
but removably mounting an object on a bone of a living patient.
[0010] As an aspect of one embodiment of the device disclosed
herein a central shaft may have a screw threaded tip to extend
through a bone and be fastened in the cortex of the opposite side
of the bone. A bone-engaging member is mounted so as to slide
longitudinally along the central shaft without being free to rotate
about the shaft and includes a sharpened front end shaped to engage
the near side of the bone securely to prevent the central shaft
from moving with respect to the bone.
[0011] As another aspect of the device, an adjustment mechanism may
include a rotatable member mounted on a screw thread formed on the
central shaft, so as to push the bone-engaging member along the
central shaft until it engages the bone, and the bone-engaging
member and the rotatable member may have mutually confronting faces
providing for rotation of the driver about the central shaft in
discrete angular steps, so as to indicate the force with which the
bone-engaging member is urged toward the bone.
[0012] As another aspect of the device the central shaft may
include a shoulder to limit the depth to which the threaded tip of
the central shaft can be engaged in a bone.
[0013] As an aspect of another embodiment of the device the central
shaft may include a combined drilling and tapping tip and a
threaded distal end portion.
[0014] A method of use of the device to removably mount an object
on a bone in accordance with the present disclosure includes
forming a hole of a first size extending into a bone for a first
distance, providing threads within the hole, placing a shaft
through the hole, and seating the shaft in the bone with a tip in
contact with a far side cortex, and thereafter forcing a
bone-engaging member longitudinally along the shaft to force a bone
gripping front end of the bone-engaging member into gripping
engagement in the bone defining and surrounding the first hole,
while providing an indication of the force being applied to move
the bone-engaging element.
[0015] One aspect of the method includes advancing the
bone-engaging element by moving it along the shaft by small
discretely defined steps.
[0016] The foregoing and other objectives, features, and advantages
of the invention will be more readily understood upon consideration
of the following detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS
[0017] FIG. 1 is a side elevational view of a device for mounting
an object removably on a bone which is an exemplary embodiment of
the present invention.
[0018] FIG. 2 is a side elevational view of a deep socket wrench
useful in operating the device shown in FIG. 1.
[0019] FIG. 3 is a perspective view of a sharpened front end of a
bone-engaging sleeve portion of the device shown in FIGS. 1 and
2.
[0020] FIG. 4 is a fragmentary oblique view of adjacent portions of
a bone-engaging member and an adjustment mechanism included in the
device shown in FIGS. 1 and 2.
[0021] FIG. 5 is a side elevational view of a portion of the device
shown in FIG. 1, with portions thereof shown in sectional view
taken on a diametrically aligned plane.
[0022] FIG. 6 is a partially cutaway view, at an enlarged scale, of
a portion of the coupling arrangement between the bone-engaging
sleeve and a sleeve-moving member of an adjustment mechanism of the
device shown in FIGS. 1, 4, and 5.
[0023] FIG. 7 is a view similar to FIG. 6 showing the coupling with
the sleeve-moving member in a different position with respect to
the sleeve.
[0024] FIG. 8 is a view of a portion of a person's upper leg,
showing a first step in the procedure of installing the mounting
device shown in FIGS. 1 and 3-7.
[0025] FIG. 9 is a view of the portion of a patient's leg shown in
FIG. 8, showing a second step in a procedure of installation of the
mounting device.
[0026] FIG. 10 is a view similar to FIG. 9, showing performance of
a subsequent step in the installation of the mounting device.
[0027] FIG. 11 is a view similar to FIG. 10 showing the mounting
device installed and in use to support an object in a fixed
position with respect to the patient's leg.
[0028] FIG. 12 is a view similar to FIG. 1 showing a device which
is an alternative embodiment of the device shown in FIG. 1.
[0029] FIG. 13 is a simplified view of a portion of a person's
upper leg, showing a first step in the procedure of installing the
mounting device shown in FIG. 12.
[0030] FIG. 14 is a view of the portion of a patient's leg shown in
FIG. 13, showing a second step of installation of the mounting
device shown in FIG. 12.
[0031] FIG. 15 is a further simplified view of the portion of a leg
shown in FIG. 14, showing the mounting device after completion of
installation.
DETAILED DESCRIPTION OF EMBODIMENTS
[0032] Referring now to the drawings which form a part of the
disclosure herein, an anchoring device 12, shown in its entirety in
FIG. 1, includes a central shaft 14. At a distal end portion 16 of
the shaft 14 a threaded tip 18 extends axially. The threaded tip 18
may be of a self-drilling, self-tapping configuration, but need not
necessarily be so. The threaded tip 18 may include a central
portion with a diameter 20 significantly smaller than a diameter 22
of the central shaft 14, and the central shaft 14 thus may define a
shoulder 24. A helical thread defined on the threaded tip 18 may
extend radially to a diameter 26 which also should be at least
slightly less than the diameter 22 for best performance.
[0033] A bone-engaging member in the form of a tubular sleeve 30 is
located on the central shaft 14 with a sliding fit. A slot 32
extends radially and longitudinally of the sleeve 30 on at least
one side thereof, and a pin 34 mounted in and extending radially
from the shaft 14 is engaged in the slot 32, so that the sleeve 30
is unable to rotate about the central shaft 14, although it is able
to move longitudinally along the shaft 14 as indicated by the arrow
36. The sleeve 30 has a bone-gripping distal end portion 38, which
may be conically tapered to a sharp edge 40, and may have sharpened
ribs 42 extending longitudinally and protruding radially from the
tapered distal end portion 38. The sleeve 30 defines a central bore
44 which should be large enough to slide easily along the central
shaft 14, but small enough to provide only a minimal amount of free
radial movement of the sleeve 30 with respect to the shaft 14. A
coupling 46 includes one or more legs 48 and interconnects the
sleeve 30 with a suitable sleeve position adjusting member, such as
a sleeve positioner 50, by engaging circumferential grooves 52 and
54 defined respectively in the sleeve 30 and the positioner 50.
[0034] The sleeve positioner 50 may have a hexagonal portion
including paired opposite flats 56 spaced a short distance away
from the groove 54, or may otherwise be configured to be engaged by
a suitable wrench, to rotate the sleeve positioner 50 about the
central shaft 14. The sleeve positioner 50 includes internal
threads engaged matingly with an external thread 58 defined on the
central shaft 14, so that rotating the positioner 50 with respect
to the central shaft 14 moves the positioner 50 longitudinally
along the central shaft 14.
[0035] One or more pins 60 or other protruding members may be
provided on the central shaft 14 near its proximal end to receive
and mate with or stabilize an object such as a portion of a
navigation system (not shown), when such an object is mounted on
the anchor device 12. Similarly, a circumferential groove 62 is
defined around the central shaft 14 near its proximal end, in order
to receive a mating device included in an object to be mounted on
the anchor device 12. A square or otherwise suitably shaped
proximal tip 64 may be provided on the central shaft 14 to mate
with a suitable power-driven wrench to rotate the central shaft 14
during installation of the anchor device 12.
[0036] A T-wrench 70 shown in FIG. 2 may include a handle 72, and
an open end 74 opposite the handle 72 is open to define a deep
socket 76 designed to mate drivingly with the flats 56 or otherwise
drivably configured portion of the positioner 50, so as to rotate
the positioner 50 with respect to the shaft 14 once the shaft 14
has been installed, as will be explained presently in greater
detail.
[0037] In one embodiment, the tapered distal end portion 38 of the
sleeve 30 may be configured as shown at an enlarged scale in FIG.
3. While a longitudinally middle portion 78 of the sleeve is
generally cylindrical, the distal or leading end portion 38 as
shown in FIG. 3 is tapered generally conically, but the several
longitudinally extending ribs 42 each has a sharp edge 80 directed
radially outwardly. For example, there may be four ribs 42 spaced
evenly about the tapered distal end 38, although as few as two or
as many as six or more ribs 42 may be useful. A leading margin
portion 82 of the tapered distal end portion 38 may be ground at a
steeper angle to form the sharp edge 40, and each of the ribs 42
may also have a tip of its distal end tapered to coincide with the
sharp edge 40 and shaped to include a sharp leading edge 86, so
that as the sleeve 30 is moved into contact with a portion of a
bone surrounding the central shaft 14 during installation of the
anchor device 12, the sharp leading edges 86 and the sharp edge 40
can engage the outer surface of the cortex of the bone and cut
slightly into the cortex of the bone so as to engage the ribs 42 in
the bone securely to prevent rotation of the sleeve 30, and thus
prevent rotation of the anchor device 12 with respect to the
bone.
[0038] Referring next to FIG. 4, the proximal face 90 of the sleeve
30 and the distal end face 92 of the positioner 50 have sets of
opposed radially extending ramp surfaces or facets which engage
each other closely at each of several positions of rotation,
determined by equally spaced radially extending ridges 94 and 95,
and corresponding notches 96 and 97. These permit the positioner 50
to rotate with respect to the central shaft 14 and the sleeve 30,
and also limit slippage of the faces 90 and 92 with respect to each
other, to provide an indication to a surgeon of when sufficient
torque has been applied to the positioner 50 to force the sleeve 30
to engage the tapered end portion 38 securely in a bone yet not
extract the threaded tip 18, as will be explained in greater detail
presently. It will be understood that the number of ridges 94 and
95 and notches 96 and 97 will determine the incremental angle of
rotation between angularly adjacent positions of engagement of the
faces 90 and 92 with respect to each other, so that in the
embodiment shown in FIG. 4, with 28 ridges 94 shown on the face 90
and 28 ridges 95 on the face 92, positions of stable engagement of
the faces 90 and 92 with each other will be separated by slightly
less than 13 degrees of rotation of the positioner 50 with respect
to the central shaft 14 and the sleeve 30.
[0039] In actual practice, the number of ridges 94 and notches 96
may be different from that shown in FIG. 4, and, for example, 40
ridges 94 and 40 notches 96 may be provided, as well as equal
numbers of ridges 95 and notches 97, with an angular separation of
9 degrees between adjacent fully mated positions of stability. For
example, each ridge 94 or 95 may have height 98 of about 0.010 inch
(0.25 mm) at the radially outer surface of the sleeve 30 and the
driver 50. While the ridges 94, 95 are shown herein as having equal
slopes of 45 degrees at the outer circumferences of the mating
faces 90 and 92, with respect to a plane 104 extending
diametrically through the sleeve 30 and a particular ridge 94, it
will be understood that other combinations of ridge height 98,
facet slopes, and angular separation of stable positions may also
be chosen. For example, a shallower angle 100 may be chosen in
combination with a steeper angle 102 in order to require more
torque to be applied to the positioner 50 in one direction of
rotation than in the other, in moving from one mated position to
the next.
[0040] As shown in FIG. 5, for example, the coupling 46 has
includes four legs 48 interconnected with each other by a belt or
ring. Each leg 48 has a catch 110 at each end, extending radially
inward and engaged in the respective groove 52 or 54. The catches
110 are separated axially apart from each other along each leg 48
by a distance 112 which is greater than the distance 114 between
the surfaces defining the nearer sides, respectively, of the
grooves 52 and 54 on the sleeve 30 and the driver 50. The distance
112 is thus great enough to allow the ridges 94 of the faces 90 and
92 to pass by each other freely, with the faces 90 and 92 separated
from contact with each other.
[0041] The coupling 46, however, prevents the positioner 50 from
being separated completely from the sleeve 30, as the catches 110
engage the shoulder surfaces defining the grooves 52 and 54.
Turning the positioner 50 in a direction in which the thread 58
moves the sleeve positioner 50 toward the proximal end of the shaft
14 thus brings the sleeve 30 along with the positioner 50, so as to
disengage the tapered distal end portion 38 of the sleeve 30 from a
bone.
[0042] As shown in FIG. 7, rotation of the positioner 50 in the
direction indicated by the arrow 116 in FIG. 7 causes the ridges 95
of the face 92 of the positioner 50 to ride up along the sloping
faces of the ridges 94 of the face 90 of the sleeve 30, which is
prevented from rotating with respect to the shaft 14 by the
engagement of the pin 34 in the slot 32 as shown in FIGS. 1 and 5.
As the opposing ridges 95 pass by the ridges 94 with continued
rotation of the positioner 50, any upward pressure on the sleeve
30, that is force urging the sleeve 30 toward the positioner 50,
will urge the ridges 94 of the face 90 of the sleeve 30 to slide
along the following slope of the ridge 95 of the face 92 of the
positioner 50 in an angular stepping manner until the ridges 94 and
grooves 97 are again mated as shown in FIG. 6, but with the sleeve
30 in a position slightly further toward the distal end 16 of the
shaft 14.
[0043] The anchor device 12 is utilized, for example, to support a
portion of an infrared navigation system on a bone in connection
with procedures such as surgical replacement of an injured knee
joint, in which case the anchor device 12 is installed in the femur
125 of a patient. To install the anchor device 12, as shown in
FIGS. 8-11, for example, soft tissue 120 is dissected and retracted
to expose a surface 122 of the anterior cortex 124 of a femur 125
as previously mentioned. A drill 126 may be used to bore a hole 128
having a diameter 130 about equal to or slightly greater than the
diameter 22 of the central shaft 14, so that the central shaft 14
can be inserted through the cortex 124 and into the marrow 132 a
short distance. The drill 126 is then retracted and, as shown in
FIG. 9, the distal end 16 of the central shaft 14 of the anchoring
device 12 is inserted into the bone through the hole 128, led by
the self drilling, self tapping threaded tip 18. Once the threaded
tip 18 engages the cortex 134 on the opposite, posterior, side of
the femur 125, the central shaft 14 is rotated to drill a hole 129
into the opposite, posterior, cortex portion 134 of the femur 125,
simultaneously tapping the hole 129 and screwing the tip 18 into
the posterior cortex 134 until the shoulder 24 at the distal end of
the shaft is brought to bear securely against the interior of the
posterior cortex 134.
[0044] When it is determined by the user, as by an increase in the
torque required to turn the central shaft 14, that the threaded tip
18 has drawn the shoulder 24 of the distal end 16 of the central
shaft 14 firmly into contact against the interior of the cortex 134
of the opposite or posterior side of the femur 125, rotation of the
central shaft 14 is stopped, and a suitable wrench, for example the
T wrench 70, is utilized to rotate the positioner 50 about the
central shaft 14. The rotation of the positioner 50 about the
central shaft 14 is accomplished initially without applying any
significant amount of torque to the central shaft 14 itself, but it
may be desirable to grasp the sleeve 30 to steady it and resist any
tendency of the sleeve and the central shaft 14 to rotate as the
positioner 50 is moved along the central shaft 14 by the threads
58. It may also be desirable to urge the sleeve 30 downward along
the central shaft 14 to keep the notched opposite faces 90 and 92
of the sleeve 30 and the positioner 50 separated from each other
until the tapered distal end portion 38 of the sleeve 30 engages
the surface 122 of the femur 125 surrounding the hole 128. As the
sleeve 30 moves downward along the central shaft 14 and through the
soft tissue surrounding the bone 125, the sleeve 30 is not required
to rotate with respect to the soft tissue 120, but only moves
downward through the soft tissue without causing unnecessary trauma
to the surrounding soft tissue 120.
[0045] Once the tapered distal end portion 38 engages the surface
122 of the anterior portion 124 of the cortex of the bone, the tips
84 of the ribs 42 begin to cut into the bone tissue surrounding the
hole 128, and by engaging the surrounding bone tissue, the ribs 42
prevent the sleeve 30 from rotating. Because the slot 32 of the
sleeve 30 is engaged with the pin 34 on the shaft 14, both the
sleeve and the shaft 14 are prevented from rotating with respect to
the bone as the wrench 70 continues to rotate the positioner 50
about the shaft 14.
[0046] As the distal end portion 38 of the sleeve 30 contacts and
penetrates the surface of the bone, the distal end face 92 of the
positioner 50 unavoidably is moved into contact against the
proximal end face 90 of the sleeve 30, bringing the ridges 95 on
the distal end face 92 into contact against the ridges 94 on the
proximal face 90 of the sleeve 30. Greater resistance to movement
of the sleeve along the shaft 14 naturally requires greater torque
to be applied to the positioner 50 to rotate it in the direction of
the arrow 116 in the next subsequent position of mating engagement
between opposing notches 94 and grooves 96. Thus, as the sharpened
tapered distal end 38 is more deeply engaged and the bone-engaging
sleeve 30 meets greater opposition from the bone it becomes more
difficult to turn the positioner 50 about the central shaft 14.
Continued rotation of the positioner 50 drives the sleeve 30 toward
the bone 125 forcing the tapered distal end portion 38 of the
sleeve 30 into deeper and firmer engagement in the anterior cortex
124 of the bone around the hole 128, but the torque required to
turn the handle 72 of the T wrench 70 increases as rotation of the
positioner 50 is continued ridge-by-ridge, until the tapered distal
end 38 is securely engaged in the bone 125 and further rotation to
move the ridges 95 through the next small angular increment, to the
next position of mating engagement in the notches 96, requires a
noticeable increase in torque to be applied to the wrench 70. At a
point before a significant increase in torque would have to be
applied to the wrench 70 to move the positioner 50 through the next
incremental angle, so that further rotation might risk extracting
the threaded tip 18 from the cortex on the far side of the bone,
the anchor device 12 will be firmly engaged in the bone 125 and
further rotation of the wrench would thereafter not be
necessary.
[0047] Once firm installation of the anchor device 12 is
accomplished, the wrench 70 may be removed and thereafter the
anchor is available for use as shown in FIG. 11 to support an
object 140 such as in infrared navigation system element, which may
be supported by the positioner 50 or otherwise engaged on the
proximal end of the central shaft 14, as by being mated with the
pins 60 or the groove 62.
[0048] As shown in FIGS. 12-15, an alternative anchoring device 150
is similar to the device 12 in many respects, but has a continuous
external thread 152 extending proximally from the distal end 154 of
its central shaft 156. Instead of having a shoulder such as the
shoulder 24 on the central shaft 14 of the device 12 described
above, the distal end 154 has a short drilling tip 158 which may be
helically fluted. A tap portion 160 which may also be fluted is
located adjacent to the drilling tip 158 and is tapered, extending
between the drilling tip 158 and the full diameter threaded portion
152 of the central shaft 156.
[0049] Use of the anchoring device 150 is somewhat simpler than use
of the anchoring device 12, as it is unnecessary to use a separate
drill to form an initial hole in the near or anterior cortex 124 of
the bone. Instead, as shown in FIG. 13, a simple opening is first
cut through the surrounding soft tissue 162 to expose the surface
of a bone such as a human femur 125 on which the device 150 is to
be installed.
[0050] Next with the sleeve positioner 50 and the sleeve 30
retracted toward the proximal end 159 of the central shaft 156, the
distal end 154 of the central shaft 156 is inserted through the
opening in the soft tissue 162, and the drill tip 158 of the anchor
device 150 is brought into contact against the surface 122 of the
anterior cortex 124. Using a suitable driver 164 to engage the
proximal end 64 of the shaft 156, the shaft 156 is rotated so that
the drill tip 158 bores a hole through the anterior cortex 124 and
the tap 160 cuts threads 166 in the anterior cortex 124, thus
forming a threaded bore through the anterior cortex 124 with the
central shaft 156 directed toward the opposite, posterior, side of
the femur 125.
[0051] With continued rotation, the external thread 152 of the
central shaft 156 becomes engaged in the threads 166, and rotation
of the central shaft is continued, moving the central shaft into
the interior of the femur 125, so that the drill tip 158 is
eventually brought to bear against the interior surface of the
posterior cortex 134, as shown in FIG. 14. Rotation of the central
shaft 156 is continued until the drill tip 158 has definitely
encountered and may have begun to cut into the cortex 134. In
reaching this position, as shown in FIG. 14, the drill tip 158 and
tap portion 160 have engaged the spongy or cancellous tissue 170
adjacent the posterior cortex 134, as can be determined by an
increase in the effort needed to rotate the central shaft 156.
[0052] Rotation of the central shaft 156 is then ceased, and a tool
such as the T-wrench 70 is then used, as described before with
respect to the mounting device 12, to engage the flats 56 of the
nut-like portion of the sleeve positioner 50 and rotate the
positioner 50 relative to the central shaft 156, thus driving the
sleeve 30 along the central shaft 156 to engage the tapered distal
end portion of the sleeve 30 in the cortex 124 of the anterior side
of the femur 125. The sleeve positioner 50 is rotated until the
slip limiting effect of the mutual contact between the ridges 94,
95 and notches 95, 97 of the faces 92 and 90 of the positioner 50
and the sleeve 30 provides definitely increased resistance to
further rotation of the positioner 50, with the tapered distal end
portion 38 of the sleeve 30 embedded in the cortex 124 far enough
so that the tips 84 and sharp edges 80 of the ribs 42 engage the
cortex 124 securely to prevent rotation of the sleeve 30 with
respect to the femur 125. As in the anchor device 12, because of
the engagement of the pin 34 extending through the central shaft
156 and engaged in the slot 32, the sleeve 30 prevents the central
shaft 156 from rotating, so that an object such as a portion of a
computer aided navigation system is held securely in its position
with respect to the femur 125 when the object is attached to the
proximal end 159 of the central shaft 156 in the same manner
described above with respect to the central shaft 14 of the
anchoring device 12.
[0053] As with the device 12, removal from engagement in the femur
125 or other bone is simply the reverse of the procedure for
mounting the anchoring device 150, as rotation of the positioning
device 50 in the opposite direction along the thread 52 on the
proximal end portion of the central shaft 156 first disengages the
torque-resisting limited slip latching faces 90 and 92 from each
other, while further movement of the positioner 50 along the
central shaft 156 causes the coupling 46 to withdraw the distal end
portion 38 of the sleeve 30 from engagement in the cortex 124 of
the femur. Once the sleeve 30 has been withdrawn from engagement in
the surface of the bone the central shaft 156 can be rotated in the
opposite direction from that used to install it and thus can be
removed from the threaded bore 168.
[0054] Because the central shaft 156 can be installed in a bone
such as the femur 125 before the sleeve 30 is moved longitudinally
along the shaft 156 through the soft tissue and toward the bone,
the soft tissue is exposed to only a limited amount of rotation of
the sleeve as the central shaft is being installed, and movement of
the sleeve along the central shaft is accomplished thereafter
without rotation, causing only a minimal amount of trauma to the
soft tissue 162 surrounding the sleeve 30.
[0055] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention in the use of such
terms and expressions of excluding equivalents of the features
shown and described or portions thereof, it being recognized that
the scope of the invention is defined and limited only by the
claims which follow.
* * * * *